Re: Fix reload1.c warning for some targets

[Jeff Law <law@redhat.com>]

On 08/05/2015 11:32 AM, Richard Sandiford wrote:
> and I don't see how GCC could prove that eliminate_regs_1 doesn't
> modify the value of recog_data.n_dups between the two loops.
> eliminate_regs_1 calls functions like plus_constant that are defined
> outside the TU and that certainly aren't pure/const.
Right.  I should have been clearer.  I don't think the reload1.c code is 
a false positive because we can't see into those functions to determine 
side effects.

> So I think c#5 (marked as a bogus reduction) is an accurate reflection
> of what reload1.c does.  c#4 looks like a genuine bug but seems different
> from the reload1.c case.  If we still warn for c#4 then I think we
> should keep the bugzilla entry open for that, but the warning for the
> reload1.c code seems justified.
Right.  I don't want to lose the false positive and associated missed 
jump threading in c#4.


  Perhaps the question is why it doesn't trigger on more targets :-)
Not sure.  Could be how match_dup is used plus some interactions with 
SRA and BRANCH_COST and who knows what else :-0


Jeff